Lean Workflow for Selection and Implementation of Smart Choke Control to Resolve Slugging in Operations

Abstract

In mature fields, pipelines are often oversized for their operating conditions. This is because their design was primarily based on the early and plateau production and less on late life production. This oversizing may lead to slugging issues, whereby flow fluctuations cause liquid handling problems in the receiving facilities, which can lead to system trips. The purpose of this paper is to describe the workflow, which includes identifying the operational problems, designing the slug control system, and commissioning and monitoring of the control system. The Smart Choke developed by Shell1 is able to mitigate the effects of slugs and has now been installed at several locations worldwide. It is an active slug control system: the topside choke acts only if surges are observed, reducing the peak flow rate into the separator. Between slugs, the choke valve opens, reducing the imposed backpressure. Since flow fluctuations are reduced, operation is again possible without risking excessive separator liquid levels. The workflow consists of the following steps: (i) If slugging leads to production deferment or to operational problems, a feasibility study is done to assess the benefits of installing a Smart Choke. To this end, the key design and production data are collected in a single data sheet that is analyzed by flow assurance experts, (ii) The analysis may include using dynamic multiphase flow models. The models are used to reproduce the slugging behaviour as seen in the field and to assess the adequacy of the Smart Choke. (iii) If the results indicate a positive outlook, and the asset agrees, the implementation needs to be planned and executed. This requires further data gathering on the choke actuator, the pipework for a suitable transducer location, and the platform control system. (iv) The flow assurance and process control experts go to the platform to help commissioning the Smart Choke, which includes tuning of the controller parameters. (v) Once in operation the Smart Choke performance is monitored remotely by the experts using PI Process Book. In addition to pipeline systems already in operation, implementation of a Smart Choke can also be considered for pipeline projects in the development phase. When in the hydraulic assessment risks are identified with respect to slugging, the decision for full implementation can be postponed, but the production system is made "Smart Choke ready" by reservation of weight/space at a pipe segment at the outlet of the pipeline upstream of the separator. When slugging occurs in a later phase of the field life the spool piece can be replaced by the required Smart Choke hardware without doing any hot work.